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  1. crutschow

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Below is the simulation with R2 removed: The low time is 88.91455ms, and the high time is 332.79446ms from the plot. Both seem close to the expected for the component values used.
  2. crutschow

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Do you mean R2 or R3?
  3. crutschow

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    My simulation is realistic in that it shows what the circuit does with the 13.7kΩ resistor I used. That value gave a low time of 668.96552ms and a high time of 665.51724ms. Using 11.2kΩ gave a low time of 576.8459ms and a high time of 667.98169ms. So for whatever reason, the value I used...
  4. crutschow

    confused about full bridge rectifier

    As BJ noted, resistance is resistance. You should be able to measure the coil resistance with either of your shitty multimeters.
  5. crutschow

    confused about full bridge rectifier

    Your confusion is that the diodes may not be blowing from overvoltage but from overcurrent.
  6. crutschow

    confused about full bridge rectifier

    Yes, I have no problem reading a schematic. I thought there may have been a connection missing since he was having problems with the diodes blowing.
  7. crutschow

    confused about full bridge rectifier

    The 1N4007 is a 1000V diode. The 1N4001 is the 50V version. Are you grounding the bridge input supply to the bridge output DC ground? If so, that will cause a dead short across a couple of the diodes and zap them. The bridge input must be completely isolated from the bridge output.
  8. crutschow

    Tachometer

    You can connect a 100nF capacitor from pin 5 to ground to filter the trigger resistor network, but it's likely not needed in this application.
  9. crutschow

    Tachometer

    Do you have an oscilloscope to view the waveforms?
  10. crutschow

    Tachometer

    The circuit I posted should be quite linear with RPM. The simulation shows an average of 1mA @ 3000 RPM and 0.1mA @ 300 RPM.
  11. crutschow

    Buck Converter Clarification

    As ramussons noted, you need a feedback loop. You can't just calculate the duty-cycles and use that, since that doesn't include all the variables in a real circuit (circuit resistance, non-linear magnetics, etc.). The duty-cycle will be close to the theoretical values you calculated, but will...
  12. crutschow

    Home theatre setup

    I've had a Rythmik 12" subwoofer (mounted in a sealed box) since around the time they first became available (I actually bought it from the garage of the person who designed the subwoofer) and have been happy with it. It has good tight bass. not boomy.
  13. crutschow

    Tachometer

    Here's an LTspice simulation of the circuit, tweaked for your requirements. As shown, the cam (lobe) output is 200pps (5ms period) for an engine speed of 3,000 RPM. The average meter current is 1.02mA (small window on left) for a U2 pot setting of 27.5kΩ.
  14. crutschow

    Tachometer

    Forgot to ask, what's the meter resistance?
  15. crutschow

    Tachometer

    How fast does the 4 lobe cam run? Is it the same as the crankshaft speed or 1/2 speed?
  16. crutschow

    Transistor switch time

    The the transistor output risetime is slow because of excess capacitive load on it's output. Reducing the collector resistor value will help that (at the expensive of more transistor current when on).
  17. crutschow

    Add one resistor to give bipolar LM555 oscillator a 50:50 duty cycle

    Yes, I have previously used that technique (simulation below): It uses a third resistor in series with the discharge transistor to equalize the charge and discharge times of the timing capacitor.
  18. crutschow

    Driving a 1930s multimeter / voltmeter dial from a software controlled source

    The input signal and the power supply must share ground (common).
  19. crutschow

    Transistor switch time

    Are you talking about the overdrive needed to switch a BJT? Below is the LTspice simulation of the 2N2222 for a 1MHz signal, with (red trace) and without (yellow trace) a base speedup capacitor. As you can see the capacitor allows it to respond to the signal, but without it, it's not fast...
  20. crutschow

    Transistor switch time

    According to the display, the oscilloscope is set to 2µs per division, not 2ms. The turn-off delay you are seeing is the storage time delay that most general purpose BJTs exhibit. A switching transistor, such as the 2N2369 will have a much shorter storage time. Alternately, a small capacitor...
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